With that said, if you get a heavier boat in the future look into either the 6.0 or 6.2 that is available in the Yukon Denali/Escalade/Suburban LTZ. I had a Denali 6.2 and it was great.

I agree with Dave. Look at the 2007 and newer Yukon XL Denali and Escalade ESV's. They are awesome.
I have owned and towed with 5.3, 6.0, and 6.2 in Suburbans, Silverados, and Yukon Denali. If you are looking for model year 2000-2006 then I would recommend the 3/4 ton Burb with the 8.1 over the 6.0 all day. You won't save at the pump for the lost performance towing and driving the 8.1. If you are looking newer, 2007 and on the best rig is the Yukon XL Denali or Cadillac Escalade ESV with 6.2. The 6.2 is excellent and comes with the heavier duty trans - 6L80E versus the 4L60 or 6L60 (in 2009) trans with the 5.3. The only way to get the 6.2 is in a Yukon Denali or Escalade.

Suburbans and Yukon XL's are the best for growing families. You just can't beat them for hauling kids, dogs, and gear plus towing your toys. That's why I just purchased another one a few weeks ago. Definitely went with the 6.2 again!!

Define growing. Are you in need of a 3rd row seat or just additional covered space?

Used to have a Suburban but we never used the 3rd seat.
Crew cab with a full topper has the same look and more function. Bed is clean and dry but if I have dirty or smelly cargo, passengers dont have to deal with it and cleanup is easy.
Plus even the short bed has more cargo space than a burb'. I wanted the long bed and have never regreted it!

My 08 Sierra with the 5.3 and 4l65e average 17 towing my little S & S from Clarksville TN to Mobile AL fully loaded down with the bed and cab full. Most have had a tail wind on the down hill drive. In 08 the 6l60 was available for the 5.3 too just didnt like the way it slid between gears and the thought of rebuilding a 6 speed over the venerable 4l60 variant

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1981 MasterCraft
19' Skier 351W PowerSlot
Long gone is the Trans AM waiting for another

I've had several vehicles that had either the 5.3, 6.0, 6.2, 8.1 or the duramax and if you plan to tow a considerable distance I would recommend something with the 6.2 or the 8.1. I've towed a X45 with a 1/2 ton GMC crew cab pickup with the 5.3, while it will tow it, I would not recommend frequent towing with the half ton unless the distance is extremely short. I also towed the X45 with a tahoe with the 5.3 and I would rather tow with the pickup vs the tahoe.
I've towed a 197 with a 3/4 ton crew cab with 6.0, 8.1 and duramax and I will say that the 8.1 pulled the boat the best. The 3/4 ton with the 8.1 had 4.11 gears and the 3/4 ton with the duramax had 3.42 gears and even with the edge chip the diesel did not compare. You couldn't tell the boat was behind you with the 8.1 and 4.11 gears. The truck would only get about 12 miles to the gallon empty or 9 while towing. I was also not impressed with the mpg of the duramax (2005) regardless of the mode it was set to.
If you don't have to tow very far then the 5.3 would be fine and will get better mpg on an avg. The 6.0 would be a good medium duty but if you tow a long distance I would definately get the 8.1 or 6.2. I'm basing this on experience from towing trailers and boats from coast to coast. So, this is based on lots of interstate travel and in town commuting.

I have a denali with the 6.0. I love it but its a gas drinker. Sure the 8.1 is worse. Depends on what you are towing though. I don't tow very far and think our longest trip was 4 hours with the boat (209). Handled it fine.........wallet did not. To be honest I'm not sure I would need more than the 6.0 but I hated towing with my buddies 5.3

I realize the gasser's (unless you get the 8.1), are weak compared to the Diesels offered by the Big Three. But, man you can buy a LOT of gas for what the diesel upgrade costs. Unless you are towing 6 days a week, that is a lot of cash to lay out to step up to the big leagues. Anyone heard if there are still oil consumption problems with the 5.3?